Question

我正在尝试编写一个捕获屏幕截图的小型库，并将图像存储在磁盘上。

我能够使屏幕截图工作，并将图像存储在磁盘上。现在，我无法根据指定的高度和宽度调整图像大小。以下是代码段：

int imageWidth = 200;
int imageHeight = 200;

CFStringRef keys[2];
CFTypeRef   values[2];
keys[0]   = kCGImagePropertyDPIHeight;
values[0] = CFNumberCreate(NULL, kCFNumberIntType, &imageHeight);
keys[1]   = kCGImagePropertyDPIWidth;
values[1] = CFNumberCreate(NULL, kCFNumberIntType, &imageWidth);


CFDictionaryRef options = NULL;
options = CFDictionaryCreate( NULL, (const void **)keys, (const void **)values, 2,
                               &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);

// Set the image in the image destination to be `image' with
// optional properties specified in saved properties dict.
CGImageDestinationAddImage(dest, imageRef, options);

bool success = CGImageDestinationFinalize(dest);
NSAssert( success != 0, @"Image could not be written successfully");

如果我做错了，请告诉我。

Answer 1

不确定，如果没有看到你如何制作CGImageRef，可能会有很多事情发生，很难看到问题。你有没有尝试使用NSImage，这非常容易使用。

NSImage * img = [[NSImage alloc] initWithCGImage:imageRef size:NSZeroSize];
[img setSize: NSMakeSize(imageWidth,imageHeight)];

//do something with img;
[img release];

如果你没有设置断点，并确保你认为有效的一切都是有效的。

Answer 2

我认为kCGImagePropertyDPIWidth和kCGImagePropertyDPIHeight不是CGImageDestinationAddImage的有意义选项。您需要创建具有给定大小的新图像，并将写入目标。

这可以通过多种方式完成，但最简单的可能是通过格雷迪建议的NSImage。您还可以创建所需大小和像素格式的新CGBitmapContext，使用CGContextDrawImage将现有图片绘制到其中，然后使用CGImageRef提取新的CGBitmapContextCreateImage。这有点乏味，但应该让你到达你想去的地方。

Answer 3

这是我的工作，不确定这是否有效。

int imageWidth  = 200;
int imageHeight = 200;

CGContextRef    context = NULL;
CGColorSpaceRef colorSpace;
void *          bitmapData;
int             bitmapByteCount;
int             bitmapBytesPerRow;

// Get image width, height. We'll use the entire image.
size_t pixelsWide = imageWidth;//CGImageGetWidth(imageRef);
size_t pixelsHigh = imageHeight;//CGImageGetHeight(imageRef);

// Declare the number of bytes per row. Each pixel in the bitmap in this
// example is represented by 4 bytes; 8 bits each of red, green, blue, and
// alpha.
bitmapBytesPerRow   = (pixelsWide * 4);
bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);

// Use the generic RGB color space.
colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);

// Allocate memory for image data. This is the destination in memory
// where any drawing to the bitmap context will be rendered.
bitmapData = malloc( bitmapByteCount );

// Create the bitmap context. We want pre-multiplied ARGB, 8-bits 
// per component. Regardless of what the source image format is 
// (CMYK, Grayscale, and so on) it will be converted over to the format
// specified here by CGBitmapContextCreate.
context = CGBitmapContextCreate (bitmapData,
                                 pixelsWide,
                                 pixelsHigh,
                                 8,      // bits per component
                                 bitmapBytesPerRow,
                                 colorSpace,
                                 kCGImageAlphaPremultipliedFirst);

// Make sure and release colorspace before returning
CGColorSpaceRelease( colorSpace );

// Get image width, height. We'll use the entire image.
size_t w = CGImageGetWidth(imageRef);
size_t h = CGImageGetHeight(imageRef);
CGRect rect = {{0,0},{imageWidth,imageHeight}}; 

// Draw the image to the bitmap context. Once we draw, the memory 
// allocated for the context for rendering will then contain the 
// raw image data in the specified color space.
CGContextDrawImage(context, rect, imageRef);

CGImageRef outImageRef = NULL;

outImageRef = CGBitmapContextCreateImage( context );

调整图像大小 - Cocoa - MAC OS X.

3 个答案: